Recovery of molybdenite from copper sulfide concentrates by froth flotation



United States Patent 3,313,412 RECOVERY OF MOLYBDENI'I'E FROM C0?- PER SULFIDE CONCENTRATES BY FROTH FLOTATIGN Philip A. Bloom and Stuart J. Hussey, Tucson, Ariz., as-

signors to the United States of America as represented by the Secretary of the Interior No Drawing. Filed Aug. 5, 1964, Ser. No. 387,813 6 Claims. (Cl. 209167) The invention herein described and claimed may be manufactured and used 'by or for the Government of the United States of America for governmental purposes without the payment of royalties thereon or therefor.

This invention relates to recovery of molybdenite from molybdenite-bearing copper sulfide ores or concentrates.

Large porphyry copper sulfide deposits containing very small amounts of molybdenite have recently become a significant source of molybdenite. Reagents used for flotation of copper minerals from these deposits also float the molybdenite in a bulk copper sulfide-molybdenite concentrate containing from 0.2 to 1.2 percent M08 To mills producing about 300 tons of copper concentrates a day this MoS represents an important source of added revenue. 1

Similar flotation characteristics of copper sulfides and molybdenite minerals and the small particle size of the copper sulfide concentrate make it difficult to separate the molybdenite and copper sulfide minerals by froth flotation. At the present time, the more popular ways used to separate these minerals are to depress the copper by drying or steaming the bulk concentrate, or using strong oxidizing agents that presumably attack the copper flotation reagents or the copper minerals, or both. These methods, however, have the disadvantage of being expensive or corrosive to equipment and in some cases in volve the use of toxic gases with an ever present hazard to employees.

It is accordingly an object of the present invention to provide a simple and eflicient method for recovery of molybdenite from molybdenite-copper sulfide ores or concentrates without excessive corrosion of equipment or hazard to employees.

It has now been found that these objectives may be accomplished by means of a flotation process in which aluminum salts are used for depression of copper sulfides without inhibiting the flotation of molybdenite.

Aluminum salts have previously been used in flotation processes; however, none of the prior art processes are analogous to applicants process and do not provide the advantages of applicants process. U.S. Patent No. 1,649,685 discloses the use of alkaline cyanides or carbonates with aluminum sulfate to separate zinc and iron sulfides. US. Patent No. 2,205,194 discloses the combination of an aluminum salt and a sulfite to form sulfur dioxide which depresses zinc sulfide. US. Patent No. 2,620,068 discloses a combination of cyanide radical, ammonia in the form of a free base and a metal from the group of magnesium, zinc or aluminum for depressing copper minerals.

The general method employed in the invention is a conventional froth flotation procedure in which the ore is first ground to fine particle size, water is then added to the pulp as required and the pulp is passed to a flotation cell where air is introduced for flotation. Reagents are added to the pulp at the grinding stage, the preflotation conditioning stage, or the flotation stage as required. In the process of the invention, the starting material may be a concentrate from a previous flotation of copper sulfide ore. The process is ordinarily carried out at room temperature and pressure using any 3,3 lBJilZ Patented Apr. ll, 1967 kind of water available, although distilled or otherwise treated water may be beneficial in some cases. The raw material employed is a copper sulfide-molybdenite ore or concentrate, the exact composition of which will vary according to the deposit from which the ore is obtained and the nature of the beneficiation to which the ore may have been subjected. Copper sulfide-molybdenite concentrates, used as starting materials in the process of the invention, are usually thickened to about 40 percent solids before conditionirn with reagents and subsequent flotation. Such concentrates will typically contain 25 to 30 percent copper and 0.6 to 0.9 percent M05 These percentages will, of course, vary with the type of ore and the flotation process employed in concentrating the copper sulfidemolybdenite minerals.

The raw material is conditioned with aluminum salt for a period of about 1 minute to about 15 minutes at a pulp density of about 25 percent to about 40 percent solids. The aluminum salt may be added as solid or in solution. Pulp density of the mixture in the subsequent rougher flotation is usually about 15 percent to about 30 percent solids, with about 25 percent solids usually being optimum.

Examples of aluminum salts that may be used are aluminum sulfate, aluminum potassium sulfate, aluminum sodium sulfate, aluminum chloride, and aluminum nitrate. Amounts of the aluminum salt will usually vary from about 1 pound per ton of ore or concentrate to about 30 pounds per ton of ore or concentrate. These variables, as well as those discussed in the preceding paragraph m-ay all vary considerably depending on the type and amount of ore or concentrate, particularly aluminum salt employed, nature of collector, if any, etc.

Addition of the aluminum salt will usually lower the pH, sometimes as low as about 4.0 to 4.5; however, the value of pH is not critical in the process of the invention. This lack of cn'ticality is, in fact, one of the ad vantages of the invention.

Although a collector is not essential in the process of the invention, separation may be enhanced by the use of a collector in conjunction with the aluminum salt. Kerosine, in an amount of from about 0.1 pound to about 4.0 pounds per ton of feed has been found to be particularly effective as a collector; however, other collectors such as fuel oil, motor oil, mineral oil, and similar petroleum products, as well as orthodichlorobenzeue, nitrobenzene, and similar benzene products, may also be used. Compounds such as pine oil, nitrobenzene, methyl isobutyl carbinol, isopropyl alcohol, n-octyl alcohol, n-decyl alcohol, and other multicarbon alcohols and their derivatives may also improve efiiciency of the process with some ores when used as frothers or froth modifiers.

It has also been found that the process of the invention may, in some instances, be further improved by the use of an alkali iron cyanide such as sodium ferrocyanide to depress copper sulfides in the final cleaning steps while employing the aluminum salts of the invention in the roughing and early cleaning steps according to the process of the instant invention. This obviates the need for using large quanities of expensive reagents, such as alkali iron cyanides, since the amount of copper sulfide left in the pulp in the final cleaning steps is relatively small compared to that in the original bulk concentrate. Use of cyanides and alkali iron cyanides in flotation recovery of molybdenite is disclosed in US. Patent No. 2,664,199.

The invention will be more specifically illustrated by the following examples.

Example 1 About a 70-liter sample of bulk copper sulfidemolybdenite concentrate thickened to about 40 percent solids was obtained from a large southwestern copper concentrator located in the vicinity of Tucson, Arizona. The sample contained 0.64 percent M and 29.83 percent Cu. The copper minerals were predominantly chalcopyrite with minor amounts of chalcocite, covellite, bornite, and metallic copper. The bulk sample was split into smaller portions containing about 540 grams. Tests were then made using no reagents, aluminum salts, and sulfuric acid. The sample of pulp was conditioned with reagents in a 600-gram laboratory float cell for a period of 5 minutes 'followed by a 12-minute flotation period to insure that most of the molbdenite floated. In the case where no reagents were added, there was no conditioning period prior to the molybdenite flotation. The residual reagents left in the bulk copper concentrate were relied on to promote the molybdenite to flotation. Table 1 gives a comparison of the results obtained using the conditions described above.

conditioner. Reagent consumption was about pounds of Al (SO and 2 pounds of kerosine per ton of feed. The results obtained are summarized in Table 3.

1 Contents are expressed as ounces per ton instead of percent.

FLOTATION OF MOS:

Concentrate ConsumppH of Reagent tion, lbs. rougher per ton Analysis, Pet. Recovery, Pct. float M08; Cu MOS; Cu

AMSOO: A 5.0 0. 83 31. 60 94. 7 79. 8 t1. 6 20. 0 1. 98 32. 55 91. 4 32. 7 3. 6 5. O 0.97 31. 28 94. 9 73. 1 6. 7 20. 0 2. 30 33. 65 92. 9 32. 1 5. 2 5.0 2.05 32.84 85.9 30. 6 3. 9 20. 0 2. 57 33. 04 91. 6 27. 9 3. 6 5. 0 0. 97 31. 90 89. 7 64. 7 6. 2 20. 0 2. 37 31. 44 41. 5 12. 0 3. 8 l5. 0 1. 38 31.03 94. 9 41. 8 4. 8 10.0 0.83 30.98 95. 5 58. 3 3. 8 0. 69 30. 86 97. 0 77. 6 7. 4 0.64 29. 83 100.0 100.0

Example 2 Example 4 Although it may be possible to eflect a good separation of molybdenite and copper sulfides by the use of aluminum salts alone, testing has revealed that better results are obtained when a molybdenite collector such as kerosine also is used. A sample similar to the one previously described was obtained and split in appropriately sized portions. The tests were made in the same type of cell and in approximately the same manner as the prior tests except a 1-minute conditioning period was used after the addition of the reagents. The first five tests of Table 2 summarize the results obtained in this series when using kerosine in addition to an aluminum salt. Good concentration of molybdenite at even higher recoveries often were obtained as illustrated in the last two tests of Table 2.

TABLE 2.-EFFECT OF KEROSINE AND ALUMINUM SULFATE ON THE COPPER SULFIDE-MOLYBDENITE About 100 gallons of a bulk copper sulfide-molybdenite concentrate similar to that used in the two prior examples was obtained for use in a small scale continuous operation. The fiowsheet was restricted to a conditioner, a rougher cell, a cleaner cell, and two scavenger cells. The middlings and scavenger froth were returned to the Using a sample similar to the one cited in Example 3 another continuous test was made differing from the previous one in that four cleaning steps were used. Reagent amounts were, in pounds per ton, 16.0 Al (SO to the conditioner, 2.6 kerosine to the conditioner, and 0.83 Al (SO to all four cleaners. In addition to these reagents a small amount of froth modifier, n-decyl alcohol, was used to help control the froth. The middlings were circulated countercurrent to the cleaner froths and finally, together with the scavenger froth, back to the conditioner. The results of this test are summarized in Table 4.

TABLE 4.RESULTS OF PILOT PLANT TEST USING FOUR CLEANING STEPS Analysis, Recovery, pct. MOS; pct. IVIOS] Example 5 to the cleaner froth and then together with the scavenger froth to the conditioner. Table 5 lists the reagent requirements and addition points. The results obtained are summarized in Table 6.

TABLE 5.REAGENT DATA Reagent, pounds per ton of feed Addition point Alg(SO4)a Kerosine K4Fe(CN) Conditioner 18. 6 2. 9 Cleaner No. 1 0.9 Cleaner No. 2 9 Cleaner No. 3 9 .2 CleanerNoul .9 .2 Cleaner No. 5 .9 2 Cleaner No. 6 .9 2

1 Small amount of n-deeyl alcohol was added to the first cleaner to reduce the volume of the froth.

2 Small amount of nitrobenzene was added to increase the froth and flotation of the molybdenite.

TABLE 6.RESULTS OF PILOT PLANT TESTING USING ALUMINUM SULFATE AND POTASSIUM FERROCYANIDE TO DEPRESS COPPER SULFIDE MINERALS Analysis Distribution Product M052 Cu M082 Cu Cleaner eoncentrate 76. 34 3. 59 81.9 10. 3 0. 15 29. 62 18. 1 89. 7

What is claimed is:

1. In a froth flotation process for the recovery of moly-bdenite from a molybdenite-copper sulfide concentrate wherein said concentrate is present in a flotation cell as an aqueous pulp, the improvement consisting of depressing the copper sulfide by adding to said aqueous pulp a depressant consisting solely of an aluminum salt and then froth floating the molybdenite.

2. The process of claim 1 in which the aluminum salt is aluminum sulfate.

3. The process of claim 1 in which kerosine is also added to the pulp as a collector for the molybdenite.

4. The process of claim 1 in which the floated molybdenite is subject to further froth flotation to obtain a cleaner concentrate.

5. The process of claim 4 in which an alkali ferrocyanide is employed as depressant for copper sulfide in obtaining the cleaner concentrate.

6. The process of claim 1 in which the amount of aluminum salt is from about 1 to about 30 pounds per ton of molybdenite containing material.

References Cited by the Examiner UNITED STATES PATENTS 1,203,372 10/1916 Lyster 209167 1,569,266 9/1924 Spearman 209167 X 2,492,936 12/1949 Nokes 209-467 2,620,068 12/ 1952 Allen 209167 2,664,199 12/1953 Barker 209167 FOREIGN PATENTS 77,571 3/1947 Russia.

HARRY B. THORNTON, Primary Examiner.

R. HALPER, Assistant Examiner. 

1. IN A FROTH PROCESS FOR THE RECOVERY OF MOLYBDENITE FROM A MOLYBDENITY-COPPER SULFIDE CONCENTRATE WHEREIN SAID CONCENTRATE IS PRESENT IN A FLOTATION CELL AS AN AQUEOUS PULP, THE IMPROVEMENT CONSISTNG OF DEPRESSING THE COPPER SULFIDE BY ADDING TO SAID AQUEOUS PULP A DEPRESSANT CONSISTING SOLELY OF AN ALUMINUM SALT AND THEN FROTH FLOATING THE MOLYBDENITE. 